once fetch link queue gets below 25 links, requeue and exit
once fetch link queue gets below 25 links, requeue and exit

the fetch_link queue works in chunks of 10k urls.  this change makes
the parent process just requeue everything without domain throttling
once the queue gets below 25.  this is to speed up the last few urls
in the queue, which can take a long time to complete due to getting
starved out by the domain throttle scheduling and also prevents a couple
of failed fetch link jobs from killing the whole topic spidering job.

berkmancenter/mediacloud,berkmancenter/mediacloud,berkmancenter/mediacloud,berkmancenter/mediacloud,berkmancenter/mediacloud